1. Field of the Invention
The present invention relates to a television broadcast receiver.
2. Description of Related Art
There have been conventionally analog broadcasting, broadcasting satellite (BS) digital broadcasting, communication satellite (CS) digital broadcasting, cable broadcasting and the like as receivable broadcast media by a television broadcast receiver. Furthermore, in recent years, ground wave digital broadcasting has also participated, and the number of receivable channels has increased more and more.
From broadcasting stations and the like which offer digital broadcasting, broadcast program information called as electronic program guide (EPG) information is also transmitted besides broadcast signals (image data and sound data) corresponding to each channel. And a user of a television broadcast receiver for digital broadcasting is enabled to select a channel suitable for his or her taste among various broadcasts with a program table based on the EPG information displayed on the display unit of the television broadcast receiver.
As television broadcast receivers acquiring the EPG information, for example, a television broadcast receiver acquiring the EPG information of all channels immediately after a power activation (see, for example, JP 2005-033567A), a television broadcast receiver acquiring the EPG information of a channel of which the EPG information should be acquired at a time when the EPG information should be acquired in accordance with a priority order based on a use history (see JP 2005-026810A), a television broadcast receiver which acquires only the EPG information which should be acquired based on the classification and the date of the EPG information and judges whether the EPG information which should be acquired have been able to be acquired without any interruption or not (see, for example JP 3607570B), and the like have been proposed.
Moreover, a television broadcast receiver acquiring EPG information by means of another reception method when the acquirement of the received EPG information has not been completed (see, for example, JP 2005-051613A), a television broadcast receiver displaying a setting screen for setting the information for receiving a broad cast signal on a display unit at the time of a power activation in the case where the information has not been set (see, for example, JP 10-042213A), and the like have been also proposed.
The television broadcast receivers mentioned above are configured to be able to store the acquired EPG information. Moreover, it is known that a time necessary for acquiring EPG information one time becomes long as the quantity of the EPG information to be acquired increases.
For example, as the television broadcast receivers disclosed in JP 2005-026810A and JP 3607570B, the time necessary for acquiring EPG information one time can be shortened in the case of acquiring only the EPG information which should be acquired. However, if the privilege of a user capable of selecting a channel suitable for his or her taste among various broadcasts is limited, the limitation is problematic.
Moreover, as the television broadcast receiver disclosed in JP 2005-033567A, when the EPG information of all channels is acquired immediately after a power activation, a user can select a channel suitable for his or her taste among various broadcasts. However, because EPG information is acquired every turning on and off of a power source even if the turning on and off are very frequently repeated, the EPG information the contents of which are hardly different from those stored in advance in spite of having acquired the EPG information over time. Consequently, the television broadcast receiver has a problem of efficiency.
On the other hand, in the North America Continent, where the ATSC digital television broadcast (hereinafter simply referred to as television broadcast) is performed, large cities are dotted on the plains. Consequently, it is possible to receive the television broadcast signals being broadcast in the suburbs of each city at other cities and middle points between the cities. Because television broadcast signals are transmitted from various directions for a user who receives the television broadcast signals, it is necessary for the user to adjust the direction of an antenna to the direction of a broadcast station from which a program which the user wants to watch is broadcast. Accordingly, multi-directional antennas such as a smart antenna are being put to practical use.
Ground wave digital broadcasting has a feature of being capable of acquiring an image having a fixed image quality by a correction and the like if the intensity of a received digital broadcasting signal is equal to a fixed threshold value or more. Consequently, watching of television broadcasts of many channels becomes possible by using the multi-directional antenna.
In addition, the following technique has been known as an apparatus connected to the multi-directional antenna such as a smart antenna.
JP 10-70502A discloses a technique enabling communications with a plurality of mobile stations with little transmission power and a small repetition frequency by suppressing the radiation of electric waves into the directions other than the direction of a mobile station with which communication is performed to remove the disturbances of the radiation to other base stations and mobile stations. To realize the communications, the technique presumes the arrival of the electric wave from the mobile station with which the communications are performed with arrival direction presumption means using the signals received by a base station to presume the direction of the mobile station, and turns the peak direction of the directivity of the directivity beam of an antenna toward the direction of the mobile station with antenna directivity control means based on the result of the presumption to suppress the radiation.
Moreover, JP 2004-15800A discloses a technique for optimizing the reception direction of an antenna by re-using a previous antenna configuration at the time of the deterioration of the performance of the antenna by a fixed amount when the reception signal after a restart or immediately after a start is smaller than a predetermined bit error rate, or when the intensity of a received signal is smaller than a predetermined intensity.
Moreover, JP 07-87011A discloses a radio communications system, a radio apparatus and a switch for performing communications with a movable body equipped with scanning means for scanning the circumference indirectly, measurement means for measuring the electric field intensity at a spot where the scanning means is located, and change means for changing the direction of a communication beam in the direction in which the strongest electric field intensity has been received by the measurement means.
According to the EIA-909 standard, the smart antenna is prescribed to have a reception direction in each division direction of a circle divided into 16 parts. A digital television broadcast signal reception apparatus receiving digital television broadcast signals is set to be able to adjust the reception direction of a multi-directional antenna to all the sixteen reception directions in conformity with the EIA-909 standard. Generally, the digital television broadcast signal reception apparatus previously performs the reception of a television broadcast signal in all of the sixteen reception directions of the multi-directional antenna for each channel capable of normal reception, and measures the signal reception intensities of the received television broadcast signals to set the direction in which the signal reception intensity is highest as the optimum reception direction of the channel.
Because the antenna on the side of a broadcasting station, i.e. the position of a transmission tower, does not change ordinarily, if the optimum reception direction is once set to each channel, it is unnecessary to reset the optimum reception direction anew. However, in the United States of America or the like, broadcasting stations are dotted in various parts of the country, and consequently the direction in which the signal reception intensity is stronger is not always the optimum reception direction in some paths of the electric waves put on the air from the electric wave towers. For example, a better image may be acquired from a television broadcast signal wave reflected by a high-rise building in comparison with the images acquired from a television broadcast signal wave disturbed by a disturbance wave caused by a power-transmission line or the like, a television broadcast signal wave which has been attenuated by passing through a forest, and the like. The patent documents mentioned above disclose no solutions to the problem.
It is an object of the present invention to provide a television broadcast receiver which can effectively acquire EPG information. Moreover, it is also an object of the invention to provide a television broadcast receiver enabling a user to select the optimum image channel to watch it without adding any special apparatus.